Power supply having interconnected voltage regulators providing multiple outputs



March 31, 1970 G. C. KENNEY ll POWER SUPPLY HAVING INTERCONNECTEDVOLTAGE REGULATORS PROVIDING MULTIPLE OUTPUTS Filed May 31, 1968 AGENT55 LOAD LOAD v bZ

0+ 6 +0- ma I O- "c 1 7V4 6 |N4 i ure 3 INVENTOR GEORGE C. KENNEY IE ElmUnited States Patent 3,504,272 POWER SUPPLY HAVING INTERCONNECTEDVOLTAGE REGULATORS PROVIDING MULTI- PLE OUTPUTS George C. Kenney H,Santa Clara, Calif., assignor to Hewlett-Packard Company, Palo Alto,Calif., a corporation of California Filed May 31, 1968, Ser. No. 733,717Int. Cl. G05f 1/58 US. Cl. 323-22 8 Claims ABSTRACT OF THE DISCLOSURE Aplurality of voltage regulators are sequentially interconnected so thatthe bias voltage required by one voltage regulator is provided by theregulated output of the immediately preceding voltage regulator. Theoutput voltages of the regulators have low ripple components. When theoutput voltage of any one of the regulators falls below its regulatedvalue, all of the voltage regulators are disabled, thereby protectingthem from overload con- 'ditions.

BACKGROUND OF THE INVENTION Frequently it is required that a powersupply provide multiple regulated outputs for supplying voltages to acombination of utilization circuits forming an integral operatingdevice. If any one utilization circuit of the combination becomesshorted or otherwise malfunctions to overload its corresponding voltagesupply, it is preferable that the entire system be turned off so as toprevent improper operation of the system and protect the other circuitsof the combination from possible damage. In addition to this protectivefeature, the power supply should provide accurately regulated outputvoltages, each of which has a low ripple component. Preferably a powersupply with these features and advantages should have a simple andeconomical circuit configuration.

SUMMARY OF THE INVENTION The present invention, in one specificembodiment, includes two or more sequentially connected voltagesregulators, each of which has a series regulating element and outputvoltage responsive control means therefor. Each regulating element andits corresponding control means are biased into operation by the outputvoltage of the immediately preceding voltage regulator. Since the biasvoltage is regulated, the ripple component at the output is low. A dropin the output voltage of any one voltage regulator due to an overloadcondition, for example, decreases the bias to the next succeedingvoltage regulator, which consequently becomes non-conducting. Thisprocess is repeated until all of the voltage regulators are turned olf.The first and last ones of the sequentially connected voltage regulatorsinclude circuit components having complementary conductivities to permitsuitable interconnection of the bias voltages.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a combined schematic andblock diagram illustrating two interconnected, reciprocally biasedvoltage regulators of one embodiment of the present invention.

FIGURE 2 is a simplified block diagram illustrating the connectionsbetween the two voltage regulators of FIG- URE 1.

FIGURE 3 is a block diagram illustrating a multiple output power supplyincluding a plurality of interconnected mutually biased voltageregulators in accordance with another embodiment of the presentinvention.

Patented Mar. 31, 1970 "ice Referring now to FIGURE 1, there are showntwo voltage regulators, the first of which includes positive andnegative input terminals 11, 13 for receiving an unregulated DC.voltage, and positive and negative output terminals 15, 17 for supplyinga regulated voltage to a load. The unregulated DC. voltage may beprovided in the conventional manner by the combination of an A.C.transformer and a four-diode bridge circuit, not shown. A filtercapacitor 19 is connected across the input terminals 11, 13.

A voltage regulating transistor 21 of the PNP type is connected inseries between the negative input terminal 13 and the negative outputterminal 17. Regulating transistor 21 is driven through its baseelectrode by an intermediate PNP type transistor 23, the two transistors21, 23 being connected in the Well-known Darlington compoundconfiguration.

The conductivities of transistors 21, 23 are varied by control meansincluding a PNP type transistor 25 having its collector electrodeconnected to the base electrode of transistor 23. The control signalproduced by transistor 25 is dependent upon the difference between areference voltage and a proportion of the regulator output voltage.Specifically, the reference voltage is provided by a Zener diode 27connected in series between the emit ter electrode of transistor 25 andthe positive output terminal 15. A proportion of the regulator outputvoltage is derived from a voltage divider formed by two resistors 29, 31connected in series between the output terminals 15, 17. The commonjunction of resistors 29, 31 is connected to the base electrode oftransistor 25. The Zener diode 27 and the three transistors 21, 23, 25are suitably biased from a negative potential source by biasing meanshereinafter described.

In operation of the above-described voltage regulator, the conductivityof transistor 21 is varied in accordarwfg? with changes in the loadingconditions between output terminals 15, 17. An increase in the load isaccompanied by a tendency for the output voltage to drop. Transistor 25is then biased toward non-conduction, and in turn transistor 21 isbiased toward greater conduction to raise the output voltage.Conversely, if the load decreases, transsistor 25 is biased towardconduction and transistor 21 conducts less. Thus, any change in loadconditions results in a compensatory change in the conduction oftransistor 21 to maintain the output voltage across terminals 15, 17constant.

The circuit configuration of the second voltage regulator is similar tothat of the first voltage regulator described hereinabove. Specifically,the second voltage regulator includes positive and negative inputterminals 33, 35 for receiving an unregulated D.C. input voltage, afilter capacitor 37, a pair of output terminals 39, 41 connectable to aload, and a main series connected voltage regulating transistor 43 ofthe NPN type. Transistor 43 is driven by an intermediate NPN typetransistor 45, and the pair of transistors 43, 45 are controlled by anNPN type transistor 47. The control signal produced by transistor 47,and thus the conductivity of transistor 43, depends on the differencebetween the reference voltage produced by a Zener diode 4'9 and thevoltage output from a voltage divider formed by resistors 51, 53. Theoperation of the second voltage regulator is substantially the same asthat previously described with respect to the first voltage regulator.

The first and second voltage regulators are reciprocally biased invariable conduction modes of operation by biasing means interconnectingthe output of each regulator with the bias input of the other regulator.Specifically, the

junction of the collector electrode of transistor 25 and the baseelectrode of transistor 23 is connected through a re-' sistor 55 to abias input terminal 57. Terminal 57 is connected to the output terminal41 of the second voltage regulator, which provides a negative biasvoltage V The voltage from terminal 57 also biases Zener diode 27 intoconduction through a resistor 59.

Similarly, the second voltage regulator receives a positive bias voltage+V through resistors 61, 63 and terminal 65, the latter of which isconnected to the output terminal 15 of the first voltage regulator.

In order to properly reference the output of each regulator for use asthe bias input to the other regulator, the output terminal 17 of thefirst regulator is connected to the opposite polarity output terminal 39of the second regulator. The two terminals 17, 39 are also connected toa common terminal 67. Thus there are provided three output voltages V VV at terminals 15, 67, 41, respectively, any one of which may serve as areference voltage. For example, if terminal 67 is grounded, voltages V Vwill have opposite polarities with respect to one another. It can beseen that the output voltages V V correspond respectively to the biasvoltages +V 2, V

It is to be noted that the bias voltage of each voltage regulator isconsiderably higher than the output voltage of the same regulator, andin the situation where the unregulated D.C-. input voltages for eachregulator are identical, the ratio of bias voltage to output voltage is2:1 for each regulator. This voltage relationship is particularlydesirable and is made possible because transistors 23, 25 andtransistors 45, 47 are of complementary conductivity types, thuspermitting the use of bias voltages of the opposite polarity.

Since the two bias voltages are regulated, the output voltages from eachregulator have low ripple components. The overall circuit configurationis simplified and incorporates a minimum number of components becauseadditional pro-regulators for the bias voltages are not required. Also,filter capacitors 19, 37 can be made considerably smaller than thoserequired in prior art voltage regulators.

An important aspect of the interconnected voltage regulators describedhereinabove is that each regulator depends for proper operation upon thebias voltage received from the other regulator. If the output of thefirst voltage regulator is shorted or overloaded so that the outputvoltage drops, the bias voltage supplied to the second regulator willalso drop thereby rendering the regulating transistor 43 non-conducting.This in turn causes a drop in the output voltage across terminals 39, 41and in the bias voltage applied to the first regulator through terminal57. Therefore, the regulating transistor 21 becomes non-conducting. Thegeneral result of the reciprocal biasing arrangement is that if onevoltage regulator is overloaded, it will disable the other voltageregulator, which in turn disables the first voltage regulator.

If both voltage regulators are disabled, due to an overload conditionfor example, they will remain disabled even after the overload conditionis removed because neither regulator is properly biased. In order toinitiate conduction of the regulating transistors 21, 43, one of thevoltage regulators, for example the second voltage regulator, isprovided with starting means including a capacitor 69, a switch 71, anda resistor 73 connected in series between the collector electrode oftransistor 47 and the common junction of input terminal 33 and thecollector electrode of transistor 45. During normal operation of thefirst and second voltage regulators, switch 71 is in the position shownin FIGURE 1 and the capacitor 69 is partially charged with a lowvoltage, on the order of 3-4 volts. When the two regulators aredisabled, regulating elements 21, 43 are non-conducting and the voltageacross capacitor 69 rises to equal the unregulated D.C. input voltageacross terminals 33, 53. The regulators are started by dischargingcapacitor 69 and then permitting this capacitor to charge through thebase-emitter junctions of transistors 43, 45, thus causing these twotransistors to conduct. This biases the first voltage regulator intooperation, which in turn properly biases the second voltage regulator,so that both regulators again operate.

The aforementioned discharging of capacitor 69 is achieved in one of twoways. Firstly, the unregulated DC. voltage may be disconnected frominput terminals 33, 35, in which case capacitor 69 discharges through aresistor 75 connected across the input terminals. Alternatively,capacitor 69 may be'discharged by momentarily moving the common arm ofswitch 71 into a position which shunts the end terminals of thecapacitor.

FIGURE 2 illustrates the previously described first and second voltageregulators in block diagram form, with their respective input, outputand biasing terminals numbered as shown in FIGURE 1. Also illustratedare the interconnections between these two voltage regulators, and theconnections providing the three output voltages V V V Theinterconnecting circuitry is not limited to two voltage regulators, butinstead may be generalized to a plurality of sequentially arrangedvoltage regulators, as shown in FIGURE 3. Specifically, the exemplaryembodiment of FIGURE 3 includes four voltage regulators, each having acircuit configuration similar to one of the first and second voltageregulators described hereinabove, and each including a pair of inputterminals for receiving an unregulated input voltage V a bias voltageinput terminal V and positive and negative output terminals. Thepositive output terminal of each regulator except the last one providesa bias voltage for the next succeeding regulator. Also, the negativeoutput terminal of each voltage regulator except the last one isconnected to the positive output terminal of the immediately succeedingvoltage regulator. The last voltage regulator of the sequentialarrangement has its negative output terminal connetced to the bias inputterminal of the first voltage regulator. Preferably, the first and lastvoltage regulators employ complementary circuit configurations, asdescribed hereinabove with respect to FIGURE 1, so that the firstvoltage regulator will operate with a negative bias and the last voltageregulator will operate with a positive bias.

The four voltage regulators of FIGURE 3 may provide as many as fiveoutput voltages V V V any one of which may be referenced to ground. Ifthe output of any one of these voltage regulators is overloaded, all ofthe regulators are disabled, due to the successive loss of bias voltagein each regulator in the manner described above with respect to FIGURE1.

What is claimed is:

1. A power supply circuit for providing multiple regulated outputvoltage comprising:

a plurality of sequentially arranged voltage regulators each including:

positive and negative input terminals for receiving an unregulatedvoltage; positive and negative output terminals for providing aregulated voltage to a load; regulating means having a variableconduction current path connected in series between one of said inputterminals and the corresponding one of said output terminals of likepolarity; means for controlling and protecting said regulating means,said controlling and protecting means including:

a source of reference voltage; driver means for varying the conductionof said current path in response to the difierence between saidreference voltage and the voltage at said output terminals means;terminal means for receiving a bias voltage; means interconnecting saidbias voltage termi nal means and said driver means for substantiallydecreasing the conduction of said current path to disable saidregulating means when said bias voltage falls below a predeterminedlevel;

means connecting the bias voltage terminal means of the first one ofsaid plurality of sequentially arranged voltage regulators to thenegative output terminal of the last one of said voltage regulators;

means connecting the positive output terminal of each of said voltageregulators other than said last voltage regulator to the bias terminalmeans of the immediately succeeding one of said sequentially arrangedvoltage regulators; and

means connecting the negative output terminal of each of said voltageregulators other than said last voltage regulator to the positive outputterminal of the immediately succeeding one of said sequentially arrangedvoltage regulators;

whereby all of said plurality of voltage regulators are disabled whenthe output voltage of any one regulator falls below said predeterminedbias voltage level.

2. The circuit of claim 1, said driver means of the first and last onesof said plurality of sequentially arranged voltage regulatorsrespectively including a transistor, said transistors being ofcomplementary conductivity type.

3. A multiple output power supply comprising:

first and second voltage regulators respectively having I one polarityand opposite polarity input terminals connectable to a source ofunregulated voltage, and one polarity and opposite polarity outputterminals connectable to a load, each of said voltage regulatorsincluding:

a regulating element having a first main current carrying electrodeconnected to one of said input terminals, a second main current carryingelectrode connected to the corresponding one of said output terminals oflike polarity, and a control electrode;

a source of reference voltage;

means connected to said control electrode for controlling the currentconduction of said regulating element in response to the differencebetween said reference voltage and a proportion of the voltage acrosssaid output terminals;

first means for biasing the regulating element of said first voltageregulator into non-conduction when the voltage across the outputterminals of said second voltage regulator falls below a predeterminedlevel, said first biasing means being connected between said onepolarity output terminal of said second voltage regulator and thecontrol electrode of said regulating element of said first voltageregulator;

second means for biasing the regulating element of said second voltageregulator into non-conduction when the voltage across the outputterminals of said first voltage regulator falls below a predeterminedlevel, said second biasing means being connected between said oppositepolarity output terminal of said first voltage regulator and the controlelectrode of said regulating element of said second voltage regulator;and

means for connecting said one polarity output terminal of said firstvoltage regulator to said opposite polarity output terminal of saidsecond voltage regulator.

4. The power supply circuit of claim 3, said controlling means for saidfirst and second voltage regulators, each including:

voltage divider means connected across the output terminals of thecorresponding one of said voltage regulators; and

a transistor having one main current carrying electrode coupled to thecorresponding one of said regulating element control electrodes; anothermain current carrying electrode connected to the corresponding one ofsaid reference voltage sources; and a control electrode connected to thecorresponding one of said voltage divider means;

said transistors of said first and second voltage regulator controllingmeans having complementary conductivities.

5. The power supply circuit of claim 4, wherein each of said first andsecond voltage regulators further includes an intermediate drivertransistor connected between the corresponding ones of said regulatingelements and said controlling means.

6. The power supply circuit of claim 4, each of said sources ofreference voltage including:

a Zener diode; and

means connected to the corresponding one of said first and secondbiasing means for biasing said Zener diode. 7. The power supply circuitof claim 3, further including starting means for initiating conductionof said regulating elements after said regulating elements are biasedinto non-conduction said starting means including:

capacitor means coupled in a series current path between the first maincurrent carrying electrode and the control electrode of the regulatingelement of one of said first and second voltage regulators; and

resistance means coupled between the input terminals of said one voltageregulator for discharging said capacitor means in the absence of anunregulated voltage across said input terminals.

8. The power supply circuit of claim 7, said starting means furtherincluding switch means for momentarily discharging said capacitor means.

References Cited UNITED STATES PATENTS 3,356,855 12/1967 Suzuki et al.3,414,802 12/1968 Harrigan et al. 323-l9 X LEE T, HIX, Primary ExaminerA. D. 'PELLlNEN, Assistant Examiner U.S. Cl. X.R. 30-752; 3'2325, 38

